For the second time in as many years, NASA researchers are using a DC-8 and other aircraft to study the effects on emissions and contrail formation of burning alternative fuels in jet engines. The Alternative Fuel Effects on Contrails and Cruise Emissions (ACCESS II) project involves flying NASA's DC-8 as high as 40,000 feet while its four CFM56 engines burn either JP-8 jet fuel, or a 50-50 blend of JP-8 and renewable alternative fuel of hydro-processed esters and fatty acids produced from camelina plant oil.

Equipment in the nose of the plane will measure wind velocity when the jet flies through the wing tip wake vortices of a DC-8. (NASA Langley/David C. Bowman)

Meanwhile, a trio of instrumented research aircraft will take turns flying behind the DC-8 at distances ranging from 300 feet to more than 10 miles in order to take measurements on emissions, and to study contrail formation as the different fuels are used. Measurements taken during ACCESS I in 2013 of the burned blended fuel showed soot emissions were reduced by 40 to 60 percent compared to JP-8 fuel by itself.

An addition to this year's ACCESS II is the plan to fly the research aircraft into the turbulent, air that streams for miles behind the DC-8's wingtips. Analysis and computer simulations were run to provide the pilots with guidance in selecting trailing distances where it's safe to fly through the vortices — which occur with every aircraft — to collect observations of exhaust composition and contrail characteristics. The goal is to collect data and sample the number particles and amount of carbon dioxide trapped within the vortices and compare that to the amount of fuel burned.